This invention relates, in general, to semiconductor materials, and more particularly, to a low temperature silicon epitaxy.
It is desirable to use low temperature (less than 900.degree. C.) processing when growing silicon epitaxial layers on a semiconductor substrate to limit the autodoping effects and the diffusion length of dopants out of the substrate. The amount or thickness of the epitaxial layer formed before the desired dopant profile is obtained is called the transition width.
The use of low temperature, however, increases the incorporation of oxygen (O.sub.2) into the silicon epitaxy. The oxygen can cause oxygen induced stacking faults or act as a contaminant which creates a barrier to electron mobility. Both of which can be detrimental to semiconductor devices formed in the silicon epitaxial layer.
It would be desirable to remove or lower the oxygen incorporation while still using a low temperature epitaxial process. A lower oxygen incorporation would increase the quality of the epitaxial layer by lowering crystal defects and raising the silicon epitaxial layer's charge carrier lifetimes.
A way of reducing the amount of oxygen incorporated into a silicon epitaxial layer is to use ultra-high vacuum CVD epitaxy, utilizing a base pressure of 1.times.10.sup.-9 torr and process pressure in the range of 1.times.10.sup.-3 torr. This ultra-high vacuum CVD process removes oxygen and water (H.sub.2 O) vapor so that less oxygen is available to incorporate into the silicon epitaxy during growth. The use of ultra-high vacuum CVD, however, in a manufacturing setting is not very practical because of low throughput and high cost.
Thus, it would be desirable to have a manufacturable process for reducing the amount of oxygen incorporation into a silicon epitaxial layer when forming epitaxial layers at low temperatures.